From WO-A1-2006/069861, a premix burner with subsequent mixing section or mixer tube (a so-called AEV burner) has been known, in which in the premix burner, which is formed according to EP-A1-704 657, a first fuel can be centrally injected and between the air inlet slots or passages which are formed by the shells in the swirler (shown clearly especially in EP-A1321 809) at least one second fuel can be introduced into the air which flows into the inner space there. In the subsequent mixer tube, provision is made for a further device for injecting a third fuel. All printed publications which are referred to here or later, and their further developments, form an integrating element of this application.
For combusting H2-rich fuels, as created for example in the form of syngas during coal gasification, it has already been proposed to inject at least some of the H2-rich fuel via the mixer tube of such a premix burner. Also, such a premix burner has already been tested with natural gas in lean premix operation, during which under high pressure H2-rich fuels with H2-to-N2 ratios of 70/30 and 60/40 have been injected in an axially staged manner in the premix burner and in the mixer tube.
During these tests, it has been shown that if a changeover is made from natural gas entirely to the H2-rich fuel, the flame migrates upstream into the mixer tube. Although the burner was able to be operated in this way without damage and with sufficiently low NOx emission, numerous disadvantages arose, however, specifically:                The pressure losses in the premix burner are increased by the factor of 3. This is undesirable in the case of gas turbines with regard to an associated gas turbine cycle.        The available mixing length, i.e. the distance between the location of the injection of the fuel and the flame front, is reduced, which leads to increased NOx-emission.        High-frequency pulsations gain in importance. In this context, it may be mentioned that the thermoacoustic vibrations represent a hazard for each type of combustion application. They lead to high-amplitude pressure vibrations, to limitation of the operating range, and they can increase pollutant emissions. This applies especially to combustion systems with low acoustic damping, as is the case for example in annular combustion chambers with reverberant walls. In order to ensure a high performance conversion over a wide operating range with regard to pulsations and pollutant emissions, provisions against these pulsations must be made.        